Tech With Galvan

Identifiers & Naming Rules

Identifiers are the names you invent — for variables, functions, classes, files. Keywords belong to Python; identifiers belong to you. But Python has rules about what counts as a legal name, and conventions about what makes a *good* one.

The three legal rules

A valid identifier:

Can contain letters, digits, and underscores: name, user2, my_score

Cannot start with a digit: 2cool ❌ but cool2 ✅

Cannot be a keyword: for ❌ but for_you ✅

Test them yourself:

code

my_name = "Galvan"       # ✅
score2 = 99              # ✅
2score = 99              # ❌ SyntaxError
my-name = "Galvan"       # ❌ SyntaxError (hyphen reads as minus!)
class = "10th"           # ❌ keyword
_class = "10th"          # ✅ (underscore prefix saves it)

That hyphen example deserves a second look: my-name = "Galvan" fails because Python reads my-name as my minus name — subtraction! Only underscores work inside names.

Case sensitivity — the classic trap

code

age = 15
Age = 20
AGE = 25

print(age, Age, AGE)     # 15 20 25 — three different variables!

age, Age, and AGE are completely unrelated names. Misspelling capitalization causes a huge share of beginner NameErrors:

code

name = "Galvan"
print(Name)              # NameError: name 'Name' is not defined

The fix is always: match the capitalization *exactly*.

The naming conventions (how good code looks)

Python won't stop you from writing x2q = 42, but the community has agreed-on styles. Follow them and your code looks professional; break them and your code *works* but reads wrong:

What	Convention	Example
Variables	lowercase_with_underscores	`total_price`, `user_name`
Constants (never change)	ALL_CAPS	`MAX_SCORE`, `PI`
Functions	lowercase_with_underscores	`calculate_total()`
Classes	CapitalWords (PascalCase)	`Student`, `BankAccount`

This style is called snake_case for variables/functions — and it's not just taste: the official Python style guide (PEP 8) specifies it, and every Python codebase you'll ever read follows it.

Names should say what they hold

The single most valuable naming advice:

code

# legal but terrible
x = 99
d = "Galvan"

# legal and clear
score = 99
student_name = "Galvan"

Future-you reads code three weeks later with no memory of writing it. x forces future-you to reverse-engineer the whole function. score explains itself. Code is read 10× more often than it's written — optimize for the reader.

One accepted exception: short names in tiny scopes are fine — for i in range(10): is universally understood.

Common Errors & Fixes

`SyntaxError: invalid syntax` on a name with a hyphen or leading digit — rename with underscores, or move the digit.

`NameError` on a variable you "already made" — capitalization mismatch. Copy-paste the exact name.

`SyntaxError: invalid syntax` with `class`, `if`, `for` as names — keyword collision; add a suffix or underscore.

✅ Checkpoint

Which are legal: my_var, 2fast, _hidden, my-var, Class? *(my_var ✅, 2fast ❌, _hidden ✅, my-var ❌, Class ✅ — it's not the keyword "class")*

Are score and Score the same variable? *(No — identifiers are case-sensitive)*

How would you name a variable holding a user's email? *(user_email — snake_case, descriptive)*

Next: comments and docstrings — how to write notes that future-you will thank present-you for.